Australian Patent Specification No. 586,341 discloses a slitted tubular valve guide insert having a substantially spiral groove along the entire length of its inner surface. At each point of intersection between the spiral groove and the slit or seam, the adjacent open ends of the substantially spiral groove are offset to create a linear discontinuity in the spiral groove. The spiral groove is, therefore, divided into a plurality of inclined groove segments. It is suggested in Australian Patent Specification No. 586,341 that by dividing the substantially spiral groove into a plurality of inclined, discrete groove segments, oil flow along the substantially spiral groove to the combustion chamber will be greatly reduced or eliminated during operation of the engine.
It has however, been found by the present inventor that during engine operation, the above arrangement suffers from a gradual leakage of oil down each of the inclined groove segments to the seam, where the accumulated oil passes downwardly to be released into the combustion chamber. Furthermore, the provision of a transverse portion to the seam does not significantly inhibit such oil flow. Whilst it is suggested that the combined effect of the oscillatory and rotational movement of the valve stem through the valve guide is to pick up and evenly spread the oil that is in the groove segments throughout the surface of the valve stem, it has been found by the present inventor that much of the oil that is within each of the groove segments is not picked up by the surface of the moving valve stem as it abuts against the innermost face of the valve guide but rather spills out into the seam.
The effect of having a succession of groove segments that open out into the seam coupled with having a single transverse portion of the seam where misalignment of the corresponding opposite edges of the sleeve is likely to occur are seen by the present inventor as the primary causes of this spillage. As a result, accumulated oil loss to the combustion chamber still occurs at unsatisfactorily high levels.
It is an object of the present invention to substantially ameliorate the disadvantages of the prior art.